$-9e + 5f - 7g + 1 = 10f + 9g + 4$ Solve for $e$.
Combine constant terms on the right. $-9e + 5f - 7g + {1} = 10f + 9g + {4}$ $-9e + 5f - 7g = 10f + 9g + {3}$ Combine $g$ terms on the right. $-9e + 5f - {7g} = 10f + {9g} + 3$ $-9e + 5f = 10f + {16g} + 3$ Combine $f$ terms on the right. $-9e + {5f} = {10f} + 16g + 3$ $-9e = {5f} + 16g + 3$ Isolate $e$ $-{9}e = 5f + 16g + 3$ $e = \dfrac{ 5f + 16g + 3 }{ -{9} }$ Swap the signs so the denominator isn't negative. $e = \dfrac{ -{5}f - {16}g - {3} }{ {9} }$